Pixel substrate and light receiving apparatus

Abstract

A pixel substrate includes a photoelectric conversion element. The photoelectric conversion element includes a doped region and a substrate region. The doped region and the substrate region form a pn junction. A pixel circuit is electrically connected to a first supply line and the photoelectric conversion element. A protection circuit is configured to short-circuit the first supply line and the substrate region when a voltage difference between the first supply line and the substrate region falls below a negative threshold voltage.

The invention claimed is: 
     
         1 . A pixel substrate, comprising:
 a photoelectric conversion element (PD) comprising a doped region and a substrate region, wherein the doped region and the substrate region form a pn junction;   a pixel circuit electrically connected to a first supply line and the photoelectric conversion element (PD), and   a protection circuit including a photoelectric current source and a main transistor circuit with a switchable current path between the first supply line and the substrate region, and wherein the photoelectric current source is configured to switch on the switchable current path to short-circuit the first supply line and the substrate region when a voltage difference between the first supply line and the substrate region falls below a negative threshold voltage.   
     
     
         2 . The pixel substrate according to  claim 1 , further comprising:
 a voltage reference terminal, wherein the substrate region and the voltage reference terminal are electrically connected through a low-resistive ohmic connection.   
     
     
         3 . The pixel substrate according to  claim 1 ,
 wherein the pixel circuit is electrically connected to a second supply line and wherein the second supply line and the substrate region are electrically disconnected.   
     
     
         4 . The pixel substrate according to  claim 1 ,
 wherein the photoelectric current source comprises a photodiode element.   
     
     
         5 . The pixel substrate according to  claim 4 ,
 wherein a total horizontal area of the photodiode element is smaller than a total horizontal area of the photoelectric conversion element (PD).   
     
     
         6 . The pixel substrate according to the  claim 1 ,
 wherein the protection circuit comprises an auxiliary transistor circuit configured to switch off the switchable current path when a voltage difference between the first supply line and the substrate region is above the negative threshold voltage.   
     
     
         7 . The pixel substrate according to  claim 6 ,
 wherein the main transistor circuit comprises a first field effect transistor, wherein the auxiliary transistor circuit comprises a second field effect transistor, and wherein the first and second field effect transistors have a same channel type.   
     
     
         8 . The pixel substrate according to  claim 7 ,
 wherein the first field effect transistor and the second field effect transistor are p-channel MOSFETs, wherein the photoelectric current source is electrically connected between a gate of the first field effect transistor and the substrate region, wherein a source/drain path of the second field effect transistor is electrically connected between the first supply line and the gate of the first field effect transistor, and wherein a gate of the second field effect transistor is electrically connected to the substrate region.   
     
     
         9 . The pixel substrate according to  claim 8 , wherein the photoelectric current source comprises a photodiode element, wherein an anode of the photodiode element is electrically connected to the substrate region and a cathode of the photodiode element is electrically connected with the gate of the first field effect transistor. 
     
     
         10 . The pixel substrate according to  claim 1 ,
 wherein the pixel substrate comprises a plurality of photoelectric conversion elements (PD) and pixel circuits.   
     
     
         11 . The pixel substrate according to  claim 1 ,
 wherein the pixel circuit comprises an amplification transistor and a transfer transistor, wherein a source/drain path of the amplification transistor is electrically connected between the first supply line and a vertical signal line (VSL), and wherein a source/drain path of the transfer transistor is electrically connected between the photoelectric conversion element (PD) and a gate of the amplification transistor.   
     
     
         12 . The pixel substrate according to  claim 1 ,
 wherein the pixel circuit comprises an amplifier portion and a feedback portion, wherein a controllable current path of the feedback portion is electrically connected between the first supply line and the photoelectric conversion element (PD), wherein a controllable current path of the amplifier portion is electrically connected between a control input of the feedback portion and the substrate region, and wherein a load element is electrically connected between the first supply line and the controllable current path of the amplifier portion.   
     
     
         13 . The pixel substrate according to  claim 1 ,
 wherein the protection circuit comprises at least two laterally separated parts electrically arranged in parallel.   
     
     
         14 . The pixel substrate according to  claim 1 , wherein the protection circuit is self-powered by the photoelectric current source. 
     
     
         15 . The pixel substrate according to  claim 1 , wherein the protection circuit is configured to limit a quiescent voltage between the first supply line and the substrate region to a voltage smaller than 100 mV when the pixel substrate is powered off and radiation impinges on the photoelectric conversion element. 
     
     
         16 . A light receiving apparatus, comprising:
 a photoelectric conversion element (PD) comprising a doped region and a substrate region, wherein the doped region and the substrate region form a pn junction;   a pixel circuit electrically connected to a first supply line and the photoelectric conversion element (PD), and   a protection circuit configured to short-circuit the first supply line and the substrate region when a voltage difference between the first supply line and the substrate region falls below a negative threshold voltage,   wherein the protection circuit comprises a photoelectric current source and a main transistor circuit with a switchable current path between the first supply line and the substrate region, wherein the photoelectric current source is configured to turn on the switchable current path when a voltage difference between the first supply line and the substrate region falls below the negative threshold voltage, and   wherein the photoelectric current source is formed on a pixel substrate.   
     
     
         17 . The light receiving apparatus according to  claim 16 , wherein the photoelectric current source comprises a photodiode element, and wherein a total horizontal area of the photodiode element is smaller than a total horizontal area of the photoelectric conversion element (PD). 
     
     
         18 . The light receiving apparatus according to  claim 16 , wherein the voltage difference between the first supply line and the substrate region falls below the negative threshold voltage when the light receiving apparatus is powered off and radiation impinges on the photoelectric conversion element (PD). 
     
     
         19 . The light receiving apparatus according to  claim 16 , wherein the protection circuit comprises an auxiliary transistor circuit configured to switch off the switchable current path when a voltage difference between the first supply line and the substrate region is above the negative threshold voltage. 
     
     
         20 . The light receiving apparatus according to  claim 19 ,
 wherein the main transistor circuit comprises a first field effect transistor, wherein the auxiliary transistor circuit comprises a second field effect transistor, and wherein the first and second field effect transistors have a same channel type.